diff --git a/src/Composer/Package/Loader/ValidatingArrayLoader.php b/src/Composer/Package/Loader/ValidatingArrayLoader.php
index 405e567f0..43f23236b 100644
--- a/src/Composer/Package/Loader/ValidatingArrayLoader.php
+++ b/src/Composer/Package/Loader/ValidatingArrayLoader.php
@@ -49,6 +49,10 @@ class ValidatingArrayLoader implements LoaderInterface
         $this->warnings = array();
         $this->config = $config;
 
+        if ($err = self::hasPackageNamingError($config['name'])) {
+            $this->warnings[] = 'Deprecation warning: Your package name '.$err.' Make sure you fix this as Composer 2.0 will error.';
+        }
+
         if ($this->strictName) {
             $this->validateRegex('name', '[A-Za-z0-9][A-Za-z0-9_.-]*/[A-Za-z0-9][A-Za-z0-9_.-]*', true);
         } else {
@@ -195,7 +199,9 @@ class ValidatingArrayLoader implements LoaderInterface
         foreach (array_keys(BasePackage::$supportedLinkTypes) as $linkType) {
             if ($this->validateArray($linkType) && isset($this->config[$linkType])) {
                 foreach ($this->config[$linkType] as $package => $constraint) {
-                    if (!preg_match('{^[A-Za-z0-9_./-]+$}', $package)) {
+                    if ($err = self::hasPackageNamingError($package, true)) {
+                        $this->warnings[] = 'Deprecation warning: '.$linkType.'.'.$err.' Make sure you fix this as Composer 2.0 will error.';
+                    } elseif (!preg_match('{^[A-Za-z0-9_./-]+$}', $package)) {
                         $this->warnings[] = $linkType.'.'.$package.' : invalid key, package names must be strings containing only [A-Za-z0-9_./-]';
                     }
                     if (!is_string($constraint)) {
diff --git a/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php b/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php
index ebe6871fe..2fc059f3c 100644
--- a/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php
@@ -298,6 +298,30 @@ class ValidatingArrayLoaderTest extends TestCase
                     'homepage : invalid value (foo:bar), must be an http/https URL',
                 ),
             ),
+            array(
+                array(
+                    'name' => 'foo/bar.json',
+                ),
+                array(
+                    'Deprecation warning: Your package name foo/bar.json is invalid, package names can not end in .json, consider renaming it or perhaps using a -json suffix instead. Make sure you fix this as Composer 2.0 will error.',
+                ),
+            ),
+            array(
+                array(
+                    'name' => 'com1/foo',
+                ),
+                array(
+                    'Deprecation warning: Your package name com1/foo is reserved, package and vendor names can not match any of: nul, con, prn, aux, com1, com2, com3, com4, com5, com6, com7, com8, com9, lpt1, lpt2, lpt3, lpt4, lpt5, lpt6, lpt7, lpt8, lpt9. Make sure you fix this as Composer 2.0 will error.',
+                ),
+            ),
+            array(
+                array(
+                    'name' => 'Foo/Bar',
+                ),
+                array(
+                    'Deprecation warning: Your package name Foo/Bar is invalid, it should not contain uppercase characters. We suggest using foo/bar instead. Make sure you fix this as Composer 2.0 will error.',
+                ),
+            ),
             array(
                 array(
                     'name' => 'foo/bar',
@@ -337,6 +361,18 @@ class ValidatingArrayLoaderTest extends TestCase
                 ),
                 false,
             ),
+            array(
+                array(
+                    'name' => 'foo/bar',
+                    'require' => array(
+                        'Foo/Baz' => '^1.0',
+                    ),
+                ),
+                array(
+                    'Deprecation warning: require.Foo/Baz is invalid, it should not contain uppercase characters. Please use foo/baz instead. Make sure you fix this as Composer 2.0 will error.',
+                ),
+                false,
+            ),
             array(
                 array(
                     'name' => 'foo/bar',